Compositions and methods for determining alloys for thermal spray, weld overlay, thermal spray post processing applications, and castings

ABSTRACT

Disclosed herein are iron-based alloys having a microstructure comprising a fine-grained ferritic matrix and having a 60+ Rockwell C surface, wherein the ferritic matrix comprises &lt;10 μm Nb and W carbide precipitates. Also disclosed are methods of welding comprising forming a crack free hardbanding weld overlay coating with such an iron-based alloy. Also disclosed are methods of designing an alloy capable of forming a crack free hardbanding weld overlay, the methods comprising the steps of determining an amorphous forming epicenter composition, determining a variant composition having a predetermined change in constituent elements from the amorphous forming epicenter composition, and forming and analyzing an alloy having the variant composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of and claims priority fromU.S. patent application Ser. No. 12/885,276, filed Sep. 17, 2010 whichwas a continuation in part of and claimed priority from U.S. patentapplication Ser. No. 12/569,713, filed Sep. 29, 2009, and furtherclaimed priority from Provisional U.S. Application Ser. No. 61/243,498,filed Sep. 17, 2009, and Provisional U.S. Application Ser. No.61/309,354, filed Mar. 1, 2010; each of which is hereby incorporatedherein by reference in its entirety for all purposes.

TECHNICAL FIELD

The present invention relates generally to metallurgy. Moreparticularly, some embodiments relate to: amorphous, nanocrystalline, ormicrocystalline metals; and weld overlay materials.

DESCRIPTION OF THE RELATED ART

Amorphous metallic materials made of multiple components with anon-crystalline structure are also known as “metallic glass” materials.The materials often have different behaviors from corresponding metalswith crystalline structures. Notably, an amorphous metallic material isusually stronger than a crystalline alloy of the same or similarcomposition. Bulk metallic glasses are a specific type of amorphousmaterials or metallic glass made directly from the liquid state withoutany crystalline phase. Bulk metallic glasses typically exhibit slowcritical cooling rates, e.g., less than 100 K/s, high material strengthand high resistance to corrosion. Bulk metallic glasses may be producedby various processes, e.g., rapid solidification of molten alloys at arate that the atoms of the multiple components do not have sufficienttime to align and form crystalline structures. Alloys with highamorphous formability can be cooled at slower rates and thus be madeinto larger volumes and can be produced using common industrialpractices such as thermal spray processing or welding. The determinationof an amorphous material is commonly made using X-ray diffractometry.Amorphous materials lack translational symmetry, and thus produce X-raydiffraction spectra composed of a single broad hump as opposed to thesharp peaks defined over a narrow diffraction angle range typical tocrystalline materials.

The formation of metallic glasses is very complex as compared toconventional crystalline materials, and thus modeling efforts designedto understand and predict production of metallic glasses are not veryaccurate. Many modeling criteria have been developed to predict certainaspects of metallic glass design. These models typically fail to includespecific quantifiable components and therefore fail to provide concretemetallic glass formation ranges. As a result, metallic glasses aredeveloped primarily through a trial and error experimental process,where many alloys must be produced and evaluated before a metallic glasscomposition is discovered.

Despite the many advantageous properties of metallic glasses, it isoften useful to contain a level of crystalline in the material rangingfrom a small fraction to completely crystalline. Nanocrystalline orfine-scale grained materials are known to contain higher hardness andstrength than equivalent larger grained materials. Metallic glasses areknown to form nanocrystalline precipitates when cooled a slower ratethan their glass forming ability requires. Even slower cooling producescomplete crystallinity ranging from nanometer sized grains and up. Ingeneral, materials which form metallic glasses have slowercrystallization kinetics and will thus form smaller grain sized thancommon materials processed under the same conditions. In additioncontrolling the rate of cooling, it is often possible to dictate thecrystallinity fraction and grain size of a material though compositionalcontrol. By altering the composition from its optimum glass formingconcentration, the precipitation of a particular crystalline phase canbe encouraged under appropriate processing conditions. This techniquehas been used to increase ductility in metallic glasses.

Most materials, even those capable of forming completely amorphousstructures under thermal spray processing, do not have slow enoughcrystallization kinetics to form an amorphous material when welded.Nevertheless, the crystallization kinetics are such that a fine-scalegrain structure is likely to form.

Most hardfacing materials, especially when dealing with weld overlayscapable of exceeding 60 Rockwell C hardness, suffer from cracking duringthe weld process as well as poor toughness. In addition to otherproblems, this cracking limits such a materials use in any applicationwhere impact occurs. Accordingly, the durability of hardfacing weldoverlays can be substantial improved by reducing the potential forcracking and increasing the overall toughness of the weld.

Using tungsten carbide (“WC”) as a hard particle reinforcement in theweld overlay technique is another typical method of hardfacing. Thistechnique involves pouring WC into the molten weld bead as thehardfacing material is being welded onto the substrate. In manyapplications this technique offers a very good hardfacing layer, howeverit is difficult to apply a hardfacing layer of this type using a hardmaterial as the matrix for the WC particles, particularly when crackingin the hardfacing layer is not desirable. Extreme wear applicationsoften demand improved wear performance beyond that which can be offeredusing a ductile matrix with WC particles, because the matrix itself islikely to wear away at an accelerated rate leaving the hard particlesexposed to shatter or pull out from the surface. Under conditions ofextreme impact as well as wear it is important to eliminate cracking inthe weld bead.

Hardbanding is a technique used to protect the drill stem duringoperation in oil and gas drilling. The hardbanding is a weld overlaymade onto a round tool joint, typically 6″ in diameter, which is appliedin the field. The hardbanding overlay is designed to be a hard wearresistant alloy which centers the drill stem within the casing, as wellas protects the drill stem from wearing itself away on the casing.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

According to certain aspects of the present disclosure, weld overlaymaterials are disclosed. In some embodiments, one or more materials ofthe present disclosure can be used as a superior weld overlay materialfor the protection of tool joints in oil and gas drilling operations. Insome embodiments, one or more materials of the present disclosure can beused for other overlay hardfacing applications.

According to certain aspects of the present disclosure, an iron-basedalloy is provided. The alloy can have a microstructure comprising afine-grained ferritic matrix. The alloy can have a 60+ Rockwell Csurface. The ferritic matrix can comprise <10 μm Nb and W carbideprecipitates.

According to certain aspects of the present disclosure, a method ofwelding is provided. The method can comprise forming a crack freehardbanding weld overlay coating with an iron-based alloy. The alloy canhave a microstructure comprising a fine-grained ferritic matrix. Thealloy can have a 60+ Rockwell C surface. The ferritic matrix cancomprise <10 μm Nb and W carbide precipitates.

According to certain aspects of the present disclosure, a method ofdesigning an alloy capable of forming a crack free hardbanding weldoverlay is provided. The method can comprise the step of determining anamorphous forming epicenter composition. The method can further comprisethe step of determining a variant composition having a predeterminedchange in constituent elements from the amorphous forming epicentercomposition. The method can further comprise forming and analyzing analloy having the variant composition.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the invention. Thesedrawings are provided to facilitate the reader's understanding of theinvention and shall not be considered limiting of the breadth, scope, orapplicability of the invention. It should be noted that for clarity andease of illustration these drawings are not necessarily made to scale.

FIG. 1A is a table illustrating a variety of atomic radii for someelements that may serve as constituents of some embodiments of theinvention.

FIGS. 1B-11 are graphs illustrating various characteristics of someembodiments of the invention.

FIG. 2 is an x-ray diffraction spectrum of an embodiment of theinvention.

FIG. 3 is an x-ray diffraction spectrum of an embodiment of theinvention.

FIG. 4 is an x-ray diffraction spectrum of an embodiment of theinvention.

FIG. 5 is an x-ray diffraction spectrum of an embodiment of theinvention.

FIG. 6 is a wear performance comparison between an embodiment of theinvention and other materials.

FIG. 7 is a coefficient of friction comparison between an embodiment ofthe invention and other materials.

FIG. 8 is a galvanic potential comparison between an embodiment of theinvention and another material.

FIG. 9 is a scanning electron microscope image of an embodiment of theinvention.

FIG. 10 is a dry sand wear test comparison between an embodiment ofinvention and other materials.

FIG. 11 is a scanning electron microscope image of the results of aVickers indentation test on an embodiment of the invention.

FIG. 12 is a scanning electron microscope image of an embodiment of theinvention.

FIGS. 13A and 13B are scanning electron microscope images of anembodiment of the invention.

FIG. 14 is a scanning electron microscope image of an embodiment of theinvention.

FIG. 15 is a scanning electron microscope image of an embodiment of theinvention.

FIG. 16 is a scanning electron microscope image of an embodiment of theinvention.

FIG. 17 is a scanning electron microscope image of an embodiment of theinvention.

FIG. 18 is MIG weld bead of alloy on 4140 steel 6″ diameter pipe showingno cracking or cross-checking as measured using liquid dye penetrant.

FIG. 19 is a diagram depicting an alloy design process according tocertain aspects of the present disclosure.

FIG. 20 is a graph illustrating an amorphous forming compositionepicenter and an associated amorphous forming composition rangeaccording to certain aspects of the present disclosure.

FIG. 21 shows an exemplary arc melter that can be used to melt anhomogeneous alloy ingot for solidification analysis.

FIG. 22 is a phase diagram that is used for predicting behavior of analloy when specific alloying elements are either added or subtractedfrom an amorphous forming epicenter composition according to certainaspects of the present disclosure.

FIG. 23 is a diagram illustrating an exemplary alloy formation andanalysis procedure.

FIG. 24 is a diagram depicting liquid composition versus cooling curvesfor various constituent compositions.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe invention be limited only by the claims and the equivalents thereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

Some embodiments are described herein in terms of structural sites. Inthese embodiments some components occupy solvent sites and others occupyprimary solute sites. In further alloys, further components occupysecondary solute sites and in some cases components occupy tertiarysolute sites. In many embodiments, the primary solute elements aredefined as the solute which are larger than the solvent elements. Forexample, the primary solute elements may be approximately as at least 5%larger than the solvent elements. FIG. 1A is a table illustrating atomicradii of various elements that may serve as components in various alloysaccording to some embodiments of the invention.

In some embodiments of the invention, a class or group of compositionsis determined using two criteria. In these embodiments, the firstcriteria is that the primary solute elements are larger than the solventelement, and the second criteria is that the thermodynamic properties ofthe compositions vary from those that would be predicted from theconstituent elements alone. As an example of the first criteria, theprimary solute element may comprise an element that is at leastapproximately 10% larger than the solvent element.

In one embodiment, a first class of alloys that satisfy these criteriamay be formed when the solvent elements comprise transition metalsranging in atomic sizes from approximately 1.27 to 1.34 Å. Asillustrated in FIG. 1A, some of these candidate elements may comprise V,Cr, Mn, Fe, Co, Ni, or Cu, for example. In this embodiment, some bulkmetallic glasses may be formed by the addition of a larger primarysolute element having an atomic size at least approximately 10% largerthan the size of the solvent element. In this embodiment, these primarysolute elements range from elements having atomic radii of at leastabout 1.41 Å for solvent elements having atomic radii of approximately1.27 Å to elements having atomic radii of at least about 1.47 Å forsolvent elements having atomic radii of 1.34 Å. For example, for Cu as asolvent, some possible candidate primary solutes comprise Mo, Pd, W, Ag,Al, Ti, or larger elements. Compositions formed according to thisembodiment may further accommodate secondary or tertiary solute elementscomprising metalloids or nonmetal elements. For example, such elementsmight comprise C, B, Si, P, N, or S. In further embodiments, this rangeof compositions may be more precisely defined according to certainthermodynamic properties.

In these embodiments, the second criteria for the class of compositionsis satisfied when the alloys have a low liquid energetic state incomparison with the energy of the solid-state. For example, deepeutectics may be used as an experimental measure of the thermodynamicstrength of the liquid in relation to the potential solid phases whichit can form. In some embodiments, these energy comparisons may beperformed by quantifying the eutectics of the compositions using acomparison between the actual melting or liquidus temperature of aspecific alloy is compared to a calculated predicted liquidustemperature of the alloy. In these embodiments, the calculated liquidustemperature may be determined using a rule of mixtures type equationusing the atomic percentages of the component elements and theirrespective pure melting temperature. For example, the calculatedliquidus temperature T, is determined according to the equationT_(c)=Σx_(i)T_(i) where x_(i) is the at. % of the component i and T_(i)is its pure melting temperature. For example, alloys within thecompositional ranges of some embodiments of the invention may havecalculated liquidus temperatures, T_(c), that are at least approximately5% greater than the actual melting temperatures of the alloys. Infurther embodiments, different ratios between actual and calculatedmelting temperatures may be used. For example, as described herein someembodiments may comprise alloys having some degree of crystallinity, forexample some alloys may comprise a micro or nanocrystalline alloys.Alloys within these embodiments may have calculated temperatures thatare, for example, at least approximately 2% or 3% greater than theactual melting temperatures of the alloys. In still further embodiments,even deeper eutectics might be desirable for some applications, such assituations where molten alloys will experience lower than typicalcooling rates. Alloys within these embodiments may have calculatedtemperatures that are, for example, at least approximately 7% or 8%greater than the actual melting temperatures of the alloys.

In some embodiments, the components of alloys may occupy distincttopological sites within the alloy. For example, a larger primary soluteelement may act as a centralized cluster site for solvent atoms to bindto during cooling. In these embodiments, these clusters allow theformation of a non-translational atomic packing scheme which resistscrystallization. Furthermore, these larger solute atoms may generateelastic strain energy in an emerging crystalline embryo lattice composedof solvent elements and increase the likelihood for such an embryo tore-dissolve instead of acting as a seed for crystallization. In someinstances, the topologies of these embodiments further allow secondaryand tertiary solute elements to occupy interstitial sites that occurbetween the dense packing clusters. In some cases, these secondary ortertiary solute elements may create strong chemical interactions withthe solvent elements.

In one embodiment, a class of metallic glass forming alloys comprisestransition metal solvents with atomic radius sizes ranging from 1.27 to1.34 Å. In this embodiment, primary solute sites may make up between 3to 20 at. % of the alloy composition. These primary solute sites may beoccupied by elements with atomic radii that are at least approximately10% larger than those of the solvent. This embodiment may furthercomprise secondary solute sites that comprise approximately 10 to 25 at.% of the alloy composition. These secondary solute sites may be occupiedby metalloid or nonmetal elements., for example C, B, Si, P, N, or S.The alloys within this embodiment further comprise alloys having meltingtemperatures that are at least approximately 5% less than a theoreticalmelting temperature calculated using a sum of the pure meltingtemperature of the components of the alloy weighted by their atomicpercentages. FIGS. 1B through 1I illustrates some characteristics ofexamples of such alloys. In these figures the alpha parameter isdetermined according to the formula

${\alpha = \frac{\sum{x_{i}T_{i}}}{T_{l}}},$

where x_(i) is atomic percent of the ith element, T_(i) is the meltingtemperature of ith element, and T_(i) is the liquidus temperature of thealloy. As these figures illustrate, alloys that form amorphousstructures tend to occur in ranges described herein.

In some alloys within this class, the number of available—oroccupied—solute sites may vary according to various characteristics ofthe components. For example, the available secondary solute site may besomewhat dependent on characteristics of the primary solute or thesolvent. For example, a primary solute that has a radius approximately15% larger than that of the solvent may allow different secondarysolutes or different amounts of secondary solutes to be used while stillretaining metallic glass forming characteristics.

In a further embodiment of the invention, a second class of alloys maycomprise alloys having solvent elements with atomic sizes in the rangeof 1.39 to 1.58 Å. For example, solvent elements within this secondclass may comprise Al, Ti, Zr, Nb, or Mo. In some instances, alloyswithin this class can accommodate a tertiary solute element in additionto primary and secondary solute elements. In this embodiment, primarysolute sites may make up approximately 10 to 30 at. % of the alloycomposition. These primary solute sites may be occupied by metallicelements having atomic radii that are at least approximately 5% smallerthan the solvent elements. These alloys may further comprise elementsmaking up 2 to 10 at. % of the alloy composition and occupying secondarysolute sites. In some embodiments, these secondary solute elements maycomprise elements having atomic radii that are at least approximately 5%larger than the solvent elements. In further embodiments, these alloysmay further comprise elements making up 5-20 at. % of the alloycomposition and occupying tertiary solute sites. These elementsoccupying tertiary solute sites may comprise metalloid or nonmetalelements such as C, B, Si, P, N, or S. Similarly to the first class ofalloys, the alloys of these embodiments may be further defined accordingto their melting temperatures, wherein their melting temperature isbelow a predetermined percentage of a theoretical integer calculatedusing a weighted sum of the pure melting temperatures of the alloy'scomponents. For example, in some embodiments the alloys may be definedaccording to a melting temperature that is at least approximately 5%less than such a theoretical temperature. In some embodiments, theaddition of this tertiary solute element may increase packing densityand thereby further increase viscosity of the alloy.

In further embodiments of the invention, the described alloys may bemodified to produce alloys forming micro or nanocrystalline structures.For example, the relative sizes or amounts of the solvents or solutesmay be varied to promote such formations. For example, the use of 1-2%more of a solvent may result in an alloys that forms a nanocrystallineor fine-grained structure instead of an amorphous structure.Additionally, the temperature requirements of some embodiments may berelaxed so that alloys having slightly higher melting temperatures, suchas 2% less than the theoretical melting temperature, may be investigatedfor micro or nanocrystalline properties. In still further embodiments,bulk metallic glass alloys may be used to form micro, nanocrystalline orpartially crystalline alloys without modification. For example, alloyswithin the above classes may be cooled at different rates or underdifferent conditions to allow at least some crystallinity in the alloy.

FIGS. 2 through 5 are x-ray diffraction spectrograms of alloysdetermined according to an embodiment of the invention. As discussedherein, in some applications may be desirable to provide compositionsthat are partially amorphous and partially nanocrystalline. For example,these coatings may be useful in wear and corrosion resistant twin wirearc spray coatings. In some applications, the coating may benefit fromhaving some limited amount of crystallinity in the coating to act as abinder phase for the remaining hard amorphous particles.

FIG. 2 is an x-ray diffraction spectrogram illustrating a twin wire arcspray coating having the following composition:

Element Fe Cr Mo C B W Ni wt percent 62 13 12 2.2 2.2 3.8 4.8 (atomic(56.3) (12.7) (6.3) (9.3) (10.3) (1)   (4.1) percent)In the illustrated coating, an amorphous phase fraction of approximately75-85% was formed in the composition. In this composition, the Fe, Cr,and Ni occupy solvent sites, the Mo and W occupy primary solute sites,and the C and B occupy secondary solute sites. Accordingly, in theillustrated embodiment, elements occupying solvent sites compriseapproximately 73 at. % of the alloy; elements occupying primary solutesites comprise approximately 7.3 at. % of the alloy; and elementsoccupying secondary solute sites comprise approximately 19.6 at. % ofthe alloy. In further embodiments, the specific elements occupying thetopological sites may vary without significantly changing the atomicpercentages of elements occupying those top logical sites. For example,in a further embodiment, an alloy may be formed by reducing thepercentage of chromium while increasing the percentage of nickel to forman alloy having a melting temperature that is approximately 5% less thanthe calculated rule-of-mixtures melting temperature. In still furtherembodiments, the percentage of occupied sites may vary. For example, theatomic percentages of elements occupying the secondary solute sites maybe increased at the expense of the elements occupying the solvent sitesto form an alloy having a melting temperature that is approximately 3%less than the calculated rule-of-mixtures melting temperature.

FIG. 3 is an x-ray diffraction spectrogram illustrating a twin wire arcspray coating having the following composition:

Element Fe Cr Nb B Ni Si Mn wt percent 65.6 14.5 8.6 4.2 4.8 1.1 1.2(atomic (56.5) (13.4) (4.5) (18.7) (3.9) (1.9) (1.1) percent)The illustrated composition has an amorphous phase fraction ofapproximately 45-55%. In this composition, the Fe, Cr, Ni, and Mn occupysolvent sites, the Nb occupies primary solute sites, and the Si and Boccupy secondary solute sites. Accordingly, in the illustratedembodiment, the elements occupying the solvent sites make upapproximately 74.9 at. % of the composition; elements occupying theprimary solute sites make up approximately 4.5 at. % of the composition;and elements occupying secondary solute sites comprise approximately20.6 at. % of the composition. As described herein, some variations ofthis alloy might comprise substituting similarly sized elements atappropriate topological sites, such as a substituting Ga for Ni; othervariations of this alloy might comprise increasing or decreasing theatomic percentages of the various sites, such as decreasing orincreasing the atomic percent of primary solute site elements by 1-5%and increasing or decreasing the atomic percent of secondary solute siteelements by a corresponding amount.

FIG. 4 is an x-ray diffraction spectrogram illustrating a twin wire arcspray coating having the following composition:

Element Fe Cr Nb B Si Mn wt percent 65.9 24.6 4.6 2.2 1.5 1.2 (atomicpercent) (59)   (23.9) (3)   (10.3) (2.7) (1.1)The illustrated composition has an amorphous phase fraction ofapproximately 35-45%. In this composition, the Fe, Cr, and Mn occupysolvent sites, the Nb occupies primary solute sites, and the Si and Boccupy secondary solute sites. Accordingly, in the illustratedembodiment, the elements occupying the solvent sites make upapproximately 84 at. % of the composition; elements occupying theprimary solute sites make up approximately 3 at. % of the composition;and elements occupying secondary solute sites comprise approximately 14at. % of the composition.

FIG. 5 is an x-ray diffraction spectrogram illustrating a twin wire arcspray coating having the following composition:

Element Fe Cr C B W Nb wt percent 67.3 9.6 2.1 1.6 8.8 10.6 (atomicpercent) (64.3) (9.8) (9.3) (7.9) (2.6)  (6.1)In this composition, the Fe and Cr occupy solvent sites, the Nb and Woccupy primary solute sites, and the C and B occupy secondary solutesites. The illustrated composition has an amorphous phase fraction ofapproximately 0-20%.

In general, amorphous phase fraction and coating hardness will varyaccording to varying spray parameters. In the embodiments illustrated inFIGS. 2-5, the coating hardness as range from approximately between 800and 1100 Vickers hardness. The particle hardness as our functions of thematerial compositions and not the coating porosity or inter particleadhesion. Typical embodiments of amorphous or nanocrystalline alloysformed within these classes have hardnesses that exceed 1200 Vickers.

FIGS. 6 and 7 are figures comparing known materials to the performanceof an alloy according to an embodiment of the invention. In thesefigures, Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8) Nb_(10.6) was comparedto a tungsten carbide/cobalt (WC/CO) having 88% at. % WC and 12 at. %Co; a first Fe-based fine grain coating comprisingFe_(balance)C_(0.04-0.06)Si_(0.6-1.5)Cr₂₅₋₃₀Ni₅₋₇Mn_(1.2-2.4)B_(3.2-3.7)(Alloy 1); and a second Fe-based fine grain coating comprisingFe_(balance)Cr_(<25)Mo_(<15)B_(<5)W_(<5)C_(<2)Mn_(<2)Si_(<2) (Alloy 2).In these comparisons, Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6)and the two other Fe-based alloys were deposited on a surface as under atwin wire arc spray coating. Due to the properties of WC/Co, thismaterial was deposited using a high velocity oxygen fuel thermal sprayprocess. As these results demonstrate, embodiments of this invention mayserve as superior materials for a variety of applications requiringhardness and wear resistance. For example, some embodiments of thisinvention may serve as superior materials for bearing coatings, or forbearings themselves.

FIG. 6 demonstrates the results of a volume loss comparison using theASTM G77 metal sliding wear test. As the figure demonstrates,Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6) had about a 0.07 mm³volume loss in the test, while WC/Co had about a 0.13 mm³ volume lossand Alloy 1 and 2 each demonstrated about a 0.17 mm³ volume loss. Asthese results demonstrate,Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6) demonstrated about an86% improvement over WC/Co and about an 142% improvement over Alloys 1and 2. As described herein, similarity in structures between thisembodiment and other embodiments of the invention are expected to resultin similar improvements.

FIG. 7 demonstrates the results of a coefficient of friction comparisonusing the ASTM G77 metal sliding wear test. As the figure demonstrates,Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6) has a coefficient offriction of about 0.53, while WC/Co and Alloy 1 each have a coefficientof friction of about 0.61, and Alloy 2 has a coefficient of friction ofabout 0.65. As these results demonstrate,Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6) demonstrated about a 15%improvement over WC/Co and Alloy 1, and a 23% improvement over Alloy 2.As described herein, similarity in structures and properties betweenthis embodiment and other embodiments of the invention are expected toresult in similar improvements.

FIG. 8 shows the results of a galvanic potential comparison between anembodiment of the invention and a comparison alloy. In this test,Fe_(65.9)Cr_(24.6)Nb_(4.6)B_(2.2)Si_(1.5)Mn_(1.2) was compared toFe_(balance)C_(0.4-0.06)Si_(0.6-1.5)Cr₂₅₋₃₀Ni₅₋₇Mn_(0.2-2.4)B_(3.2-3.7)in a seawater galvanic cell with 316 stainless steel serving as areference electrode. The alloy according to an embodiment of theinvention demonstrated a galvanic potential of about −275 mV as comparedto about −375 mV forFe_(balance)C_(1.04-1.06)Si_(6-1.5)Cr₂₅₋₃₀Ni₅₋₇Mn_(1.2-2.4)B_(3.2-3.7).These results demonstrate the superiority of some embodiments of theinvention in corrosive environments, such as seawater. The resultsdemonstrate that some embodiments of the invention have potentialssimilar to that of 400 series stainless steels. Accordingly, embodimentsof the invention may serve as superior wear resistant coatings inapplications such as ship hulls where traditional Fe-based coatings,even corrosive resistant coatings such asFe_(balance)C_(0.04-0.06)Si_(0.06-1.5)Cr₂₅₋₃₀Ni₅₋₇Mn_(1.2-2.4)B_(3.2-3.7),degrade too rapidly.

In various embodiments, many different materials may be formed using themethods described herein. For example, bulk metallic glass formingmaterials may be determined according to the formulaFe₆₂₋₆₆Cr₁₃₋₂₅(Mo,Nb)₄₋₁₂(C,B)_(2.2-4.4)Ni_(0-4.8)Si_(0-1.5)Mn_(0-1.2)W_(0-3.8),and particularly according to the formulaeFe₆₂₋₆₆Cr₁₄₋₁₆Nb₈₋₁₀B_(4-4.4)Ni_(3-4.8)Si_(0-1.1)Mn_(0-1.2) andFe₆₀₋₆₆Cr₂₀₋₂₅Nb₄₋₅B₁₋₃Si_(1-1.5)Mn₁₋₂. In further embodiments,composite materials may be formed by combining components that areformed according to these formulae.

As described herein, adjusting some parameters may result in materialsthat form nanocrystalline or fine grained structures. For example, suchnanocrystalline or fine grained structure may comprise materials definedby the formulaFe₆₇₋₆₉Cr_(9.6-10.9)(Mo,Nb)_(9.2-10.6)C_(1.4-2.1)B_(1.6-1.8)Si_(0-0.2)Ti_(0-0.2)W_(7.3-9),and more particularly according to the formulaeFe₆₇₋₆₉Cr_(9.6-10.9)C_(1.4-2.1)B_(1.6-1.8)W_(7.3-9)Nb_(9.2-10.6) andFe₆₇₋₆₉Cr_(9.6-10.9)Mo_(4-5.3)C_(1.4-2)B_(1.6-0.8)W_(7.3-9)Nb_(4-5.3).In further embodiments, composite materials may be formed by combiningcomponents that are formed according to these formulae. In still furtherembodiments, other amorphous forming materials may be similarly modifiedto result in materials that form nanocrystalline or fine grainedstructures.

In additional embodiments, composite materials may be made that tend toform partially amorphous and partially nanocrystalline or fine grainedstructures. For example, one or more components defined by the aboveformulae for amorphous structured materials may be combined with one ormore components defined by the above formulae for nanocrystalline orfine grained structured materials. In a specific embodiment, such amaterial may comprise a mixture of components selected from the groupcomprising:

(1) Fe₆₂Cr₁₃Mo₁₂C_(2.2)B_(2.2)W_(3.8)Ni_(4.8),

(2) Fe_(65.9)Cr_(24.6)Nb_(4.6)B_(2.2)Si_(1.5)Mn_(1.2),

(3) Fe_(65.6)Cr_(14.5)Nb_(8.6)B_(4.2)Ni_(4.8)Si_(1.1)Mn_(1.2),

(4) Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6), and

(5) Fe_(63.4)Cr_(9.4)Mo_(12.5)C_(2.5)B_(1.8)W_(10.4).

As described herein, some alloys that have a tendency to form amorphousor partially amorphous structures in some conditions are likely to formfine-grained weld overlays. Accordingly, some embodiments of theinvention demonstrate improved hardness and toughness in hardfacewelding applications. FIG. 9 is a scanning election microscope (SEM)image of an alloy according to an embodiment of the invention,Fe_(67.5)Cr_(9.6)C_(2.1)B_(1.6)W_(8.8)Nb_(10.6), demonstrating this finegrain structure in a weld overlay coating. FIG. 10 illustrates theresults of a test comparing the alloy of FIG. 9 to a first Fe-based finegrain coating comprisingFe_(balacne)C_(0.04-0.06)Si_(0.6-5)Cr₂₅₋₃₀Ni₅₋₇Mn_(1.2-2.4)B_(3.2-3.7)(Alloy 1) and a second Fe-based fine grain coating comprisingFe_(balance)Cr_(<25)Mo_(<15)B_(<5)W_(<5)C_(<2)Mn_(<2)Si_(<2) (Alloy 2).As illustrated, the alloy according the embodiment of the inventiondemonstrates a mass loss of about 0.07 G, compared to about 0.14 G forAlloy 1 and about 0.26 G for Alloy 2. Accordingly, the alloy of theembodiment of the invention demonstrates around a 100% to 200%improvement over Alloys 1 and 2.

In some hardfacing applications, WC or other hard particles are used asreinforcing the weld overlay. For example, coarse hard carbide particlesmay be introduced into the weld bead as it is being deposited. Someembodiments of the invention allow enable hardfacing weld overlays to beformed using WC or other hard particle reinforcement without significantcracking or decreased toughness. Furthermore, when these embodiments areused for the matrix of such reinforced weld overlays, they retain thehardness and wear resistance described herein. FIG. 11 is an SEM imagedemonstrating the results of 1000 kg load Vickers indentation on ahardfacing weld overlay comprising a matrix of an alloy formed accordingto an embodiment of the invention and coarse carbide particles. In thistest, Fe_(75.1)Cr₁₀Nb₁₀B_(4.65)Ti_(0.25) was used as a matrix for coarsecarbide particles where the coarse carbide particles constituted 50% byvolume of the weld overlay. These test results demonstrate the toughnessof some embodiments of the invention; even under a 1000 kg load Vickersindentation, there was no cracking at the interface between the carbideparticles and the matrix. FIG. 12 is an SEM showing a portion of thisinterface. As this figure illustrates, the hard carbide particlesreprecipitate at the interface as opposed to dissolving into the matrix,which would otherwise introduce brittleness into the matrix. FIG. 13 isa further illustration of the toughness of a carbide reinforced weldoverlay according to an embodiment of the invention. FIG. 13Ademonstrates the fine grain structure of a carbide reinforced weldoverlay comprising Fe_(75.1)Cr₁₀Nb₁₀B_(4.65)Ti_(0.25). FIG. 13Billustrates a further 1000 kg load Vickers indentation test, againdemonstrating an absence of cracking at the interface between thecarbide particles and the matrix.

Further embodiments of the invention comprise ranges of alloys thatdemonstrate precipitation of a substantial fraction of hard carbideparticles in carbide reinforced weld overlays. In one of theembodiments, a range of alloys is defined by the formula:Fe₆₇₋₇₁Cr_(9.6-9.7)(Mo,Nb)_(8.8-10.6)C_(1.8-2.2)B_(1.4-1.6)W_(7.4-8.8).For example, the alloy discussed with respect to FIGS. 9 and 10 is analloy within this embodiment. In a further embodiment, the range ofalloys comprises alloys defined by the formulaFe₆₇₋₇₁Cr_(9.6- 9.7)Mo_(8.8-10.5)C_(1.8-2.2)B_(1.4-1.6)W_(7.4-8.8). Infurther embodiments, an alloy may be made up of a plurality ofcomponents, wherein one or more of the components comprises alloysdefined by these formulae. Materials formed according to theseembodiments have typical hardnesses of 1300-1450 Vickers hardnessthroughout the entire microstructures.

In another embodiment of the invention, a material that is suitable forhard particle reinforcement weld overlays comprises a component definedby the formulaFe₄₃₋₅₄Cr_(5.7-7.2)(Mo,Nb)_(6.6-15.5)C_(1-1.3)B_(1-1.8)W_(9.98-28)Ti₁₋₇.In further embodiments, such a component may be defined by the formulaFe_(50.5-53.2)Cr₆₋₇₂Mo_(6.6-7.9)C_(1.3-1.6)B_(1-1.2)W_(25-26.6)Ti₃₋₅. Inadditional embodiments, a component of a material may be definedpartially by the first formula and partially by the second. For example,a component might comprise Fe₅₂Cr_(5.7)Mo_(8.9)C_(1.1)W_(26.2)Ti_(6.1).In still further embodiments, an alloy comprises a plurality ofcomponents, wherein the components are each defined by one of the aboveformulae. Embodiments of the invention formed according to theseformulae may demonstrate substantial precipitation of hard particles inreinforced weld overlay applications. For example, FIG. 14 is a SEMdemonstrating the precipitation of WC particles in a slow quenched ingothaving a matrix comprisingFe_(43.2)Cr_(5.7)Mo_(15.5)C_(1.8)B_(1.3)W_(27.5)Ti₅. FIG. 14 furtherdemonstrates that alloys formed according to these embodiments retain afine-grained microstructure even under slow cooling conditions.Materials formed according to these embodiments have typical hardnessesof 1300-1450 Vickers hardness throughout the entire microstructures.

In one embodiment of the invention, a material that demonstrates hardparticle precipitation comprises a component defined by the formulaFe₅₄₋₇₅Cr_(9-14.4)Ni_(0-4.8)(Mo,Nb)_(7.9-19.7)C_(1.6-2.1)B_(1.3-4.6)W_(0-9.98)Ti_(0.25-7)Si_(0-1.1)Mn_(0-1.1).FIG. 15 demonstrates that a component comprisingFe_(54.6)Cr_(7.2)Mo_(19.7)C_(2.1)B_(1.1)W_(9.5)Ti₅ demonstratesprecipitation of a high fraction of embedded hard particles during slowcooling. FIG. 15 further demonstrates the fine-grained nature of theseembodiments that occur in non-amorphous phase forming conditions. In afurther embodiment of the invention, materials may be formed having acomponent that is defined by the formulaFe₇₀₋₇₅Cr₉₋₁₀Nb₇₋₁₀B_(4-4.6)Ti_(0.25-7),Fe₅₄₋₆₃Cr_(7.2-9.6)Mo_(8.6-19.7)C_(0.6-2.1)B_(1.1-1.7)W_(8.5-9.5)Ti₃₋₇.Additionally, in some embodiments, materials may be formed havingcomponents that comprise combinations of these formulae. Materialsformed according to these embodiments have typical hardnesses of1300-1450 Vickers hardness throughout the entire microstructures.

In further embodiments of the invention, materials may be formed thatcomprise mixtures of alloys formed according to the formulae describedherein. For example, a material may be formed comprising a plurality ofcomponents that are defined by the formulaeFe₅₄₋₇₅Cr_(9-14.4)Ni_(0-0.8)(Mo,Nb)_(7.9-19.7)C_(1.6-2.1)B_(1.3-4.6)W_(0-9.98)Ti_(0.25-7)Si_(0-1.1)Mn_(0-1.1)andFe₄₃₋₅₄Cr_(5.7-7.2)(Mo,Nb)_(6.6-15.5)C_(1-1.3)B_(1-1.8)W_(9.98-28)Ti_(1.7).In a specific embodiment, a material comprises a mixture of one or moreof the following components:

(1) Fe_(67.5)Cr_(9.6)Mo_(5.3)C_(2.1)B_(1.6)W_(8.8)Nb_(5.3),

(2) Fe₆₉Cr_(10.9)Nb_(9.2)B_(1.8)C_(1.4)W_(7.3)Si_(0.2)Ti_(0.2),

(3) Fe_(67.5)Cr_(9.6)Mo_(10.5)C_(2.2)B_(1.6)W_(8.8),

(4) Fe_(70.9)Cr_(5.7)Mo_(8.8)C_(1.8)B_(1.4)W_(7.4),

(5) Fe_(43.2)Cr_(5.7)Mo_(15.5)C_(1.8)B_(1.3)W_(27.5)Ti₅,

(6) Fe_(50.5)Cr_(7.2)Mo_(7.9)C_(1.6)B_(1.2)W_(26.6)Ti₅,

(7) Fe_(53.2)Cr_(7.3)Mo_(6.6)C_(1.3)B₁W_(25.6)Ti₅,

(8) Fe_(50.3)Cr_(7.2)Nb_(7.9)C₂₋₆B_(1.2)W_(25.8)Ti₅,

(9) Fe_(57.2)Cr_(7.3)Mo_(6.6)C_(1.3)B₁W_(25.6)Ti₁,

(10) Fe_(51.2)Cr_(7.3)Mo_(6.6)C_(1.3)B₁W_(25.6)Ti₇,

(11) Fe_(54.6)Cr_(7.2)Mo_(19.7)C_(2.1)B_(1.1)W_(9.5)Ti₅,

(12) Fe_(67.4)Cr_(9.6)Mo_(9.4)C_(1.8)B₂W_(8.8)Ti₁,

(13) Fe₆₃Cr_(9.6)Mo_(8.6)C₁₋₆B_(1.7)W_(8.8)Ti₇,

(14) Fe_(70.2)Cr_(9.6)Mo_(8.7)C_(1.7)B_(1.4)W_(7.4)Ti₁,

(15) Fe₆₆Cr₉Mo_(8.2)C_(1.6)B_(1.3)W_(6.9)Ti₇,

(16) Fe_(75.1)Cr₁₀Nb₁₀B_(4.65)Ti_(0.25),

(17) Fe_(74.6)Cr_(9.9)Nb_(9.9)B_(4.6)Ti₁,

(18) Fe₇₀Cr_(9.3)Nb_(9.3)B_(4.4)Ti₇,

(19) Fe_(64.9)Cr_(14.4)Nb_(8.5)B_(4.8)Ni_(4.1)Ti₁Si_(1.1)Mn_(1.2),

(20) Fe₆₁Cr_(13.5)Nb_(7.9)B_(4.5)Ni₄Ti₇Si₁Mn_(1.1),

(21) Fe_(63.8)Cr_(9.6)Nb_(11.7)C_(2.1)B_(1.8)W₁₀Ti₁,

(22) Fe_(62.3)Cr_(9.6)Nb_(9.6)C_(1.9)B_(1.5)W_(8.1)Ti₇.

In a process according to one embodiment of the invention, coarse hardparticles are combined with a hard matrix material comprising componentsdescribed herein. This process comprises melting a component asdescribed herein over a layer of coarse particles. For example, an arcmelter may be used to melt a matrix material over a bed of coarse WCparticles. In some embodiments, although melted WC may have a tendencyto reprecipitate, it is desirable to minimize the amount of WC thatdissolves into the melted matrix. In one embodiment, the coarseparticles are disposed on a cooling body, such as a grooved hearth. Forexample, a water-cooled grooved copper hearth may be used. In thisembodiment, the coarse particles are kept at a lower temperature toincrease their resistance to dissolution. Accordingly, in theseembodiments, the WC particles are allowed to metallurgically bind to thematrix without substantially dissolving into the matrix.

In particular experiments, this procedure was conducted using 30%, 40%,and 50% by weight coarse tungsten carbide particles, wherein theremaining weight percentages comprised a matrix material comprisingcomponents described herein.

FIGS. 16 and 17 are SEM images demonstrating typical results of theseexperiments. FIG. 16 illustrates a typical result where 4-8 mesh 80-20WC/Co was used as the hard particle, forming a composite material:Fe_(37.6)Cr₅Nb₅C_(1.8)B_(2.4)W_(42.2)Co₆. As this figure indicates, thematrix forms a metallurgical bond with the WC/Co particle withoutsubstantially dissolving the particle into the matrix. FIG. 17illustrates a typical result where 4-8 mesh 88-12 WC/Co particles servedas the hard particle, forming a composite material:Fe_(52.7)Cr₇Nb₇C₁B_(3.3)W₂₃Co₆. This figure also demonstrates ametallurgical bond between the WC/Co particle and the matrix, withoutsubstantial dissolution of the particle into the matrix. The materialsformed according to this embodiment are Fe and W based compositionscomprising composite materials of WC hard particles embedded in a hardmatrix. In these experiments, the Vickers hardness of the WC isapproximately 1400, while the matrix demonstrated Vickers hardnesses ofapproximately 1200 due to some dissolution of the coarse particles intothe matrix. The materials also demonstrate resistance to cracking at theinterface between the particles and the matrix. Accordingly, thesematerial are well-suited for applications where both extreme impact andextreme abrasive wear occur. In some embodiments, these materials may bepre-formed for use as components in other applications. As the materialscool, they may contract. Accordingly, the cooling surfaces, such as thegrooved hearth, will typically be adjusted for such contractions.

In some embodiments, these composite materials may be formed usingcomponents defined by the formula(Fe_(54.6-75.3)Cr_(7.2-24.6)Mo_(0-19.7)C_(0-2.3)B_(1.5-4.7)W_(0-9.5)Nb₀₋₁₀Ti₀₋₇Si_(0-1.5)Mn_(0-1.2))_(x)(W_(76.8-84.5)C_(3.2-3.5)Co₁₂₋₂₀)_(100-x)where x=50-70. In these embodiments, a matrix material may therefore bedefined by the formulaFe_(54.6-75.3)Cr_(7.2-24.6)Mo_(0-19.7)C_(0-2.3)B_(1.5-4.7)W_(0-9.5)Nb₀₋₁₀Ti₀₋₇Si_(0-1.5)Mn_(0-1.2).In some specific embodiments, a composite material comprises one or morecomponents defined by the formulae:

(1) Fe_(38.2)Cr₅Mo_(13.8)C_(2.7)B_(1.2)W₃₂Ti_(3.5)Co_(3.6)

(2) Fe_(27.2)Cr_(3.6)Mo_(9.9)C_(2.9)B_(0.9)W_(4.7)Ti_(2.5)Co₆

(3) Fe_(38.2)Cr₅Mo_(13.8)C_(2.7)B_(1.2)W₃₂Ti_(3.5)CO_(3.6)

(4) Fe₃₂Cr_(4.6)Mo₅C_(2.6)B_(0.8)W_(42.5)Ti_(2.5)Co₁₀

(5) Fe_(52.7)Cr₇Nb₇C₁B_(3.3)W₂₃Co₆

(6)Fe_(46.2)Cr_(17.2)Nb_(3.2)C_(1.1)B_(1.5)W_(25.3)Ti_(3.2)Si_(1.1)Mn_(0.8)Cu_(3.6)

(7) Fe₄₉Cr_(6.5)Nb_(6.5)C_(1.1)B_(3.1)W_(25.3)Co₆Ti_(4.9)CO_(3.6)

(8) Fe_(37.6)Cr₅Nb₅C_(1.8)B_(2.4)W_(42.2)Co₆

In further embodiments, other materials disclosed herein may serve assuitable matrix materials. For example, the compounds described abovewith respect to weld overlay applications may serve as suitable matrixmaterials for these composite materials.

As described herein, a variety of elements may occupy solvent sites invarious embodiments of the invention. For example, both Fe and Ni havean atomic radius of 128 Å. Accordingly, Ni may be substituted for someor all of an amount of Fe in the materials and components describedherein. For example, in the material described with respect to FIG. 3,Fe_(65.6)Cr_(14.5)Nb_(8.6)B_(4.2)Ni_(4.8)Si_(1.1)Mn_(1.2), arbitraryamounts of Ni may be substituted for arbitrary amounts of Fe, such thatthe melting temperature of the resultant alloy remains at leastapproximately 5% less than the melting temperature predicted by a ruleof mixtures. In some embodiments, these materials containing Ni may beparticularly well-suited for brazing applications. In particularembodiments, these brazing alloys comprise alloys having componentsdefined by the formula (Ni,Fe)₅₀₋₉₅(Si,B,P)₀₋₂₀Cr₀₋₃₅. In furtherembodiments the relationship between Ni and Fe may be further definedaccording to the methods and processes described herein, such asinspection of melting temperatures compared to rule of mixture meltingtemperatures. In a specific embodiment, such a braze material comprisesat least one component selected from the group comprisingNi₅₂B₁₇Si₃Fe₂₈, Ni₅₅Bi₈Cr₄Fe₂₄, Ni₅₄B₁₄Si₄, Cr₄Fe₂₄, Ni₅₂B₂₀Fe₂₈, andFe₄₃Cr₃₃Ni₁₀B₁₄.

In additional embodiments, the alloys may further contain additives toenhance or introduce various features. For example, small amounts of Al,Ca, Y, misch metal, or other materials may be added as oxygen getters.In the above formula, the addition of these oxygen getters results inthe formula (Ni,Fe)₅₀₋₉₅(Si,B,P)₀₋₂₀Cr₀₋₃₅(Al, CA,Y,misch)₀₋₁, or moreparticularly (Ni,Fe)₅₀₋₉₅(Si,B,P)₀₋₂₀Cr₀₋₃₅(Al,CA,Y,misch)_(0-0.2).

In further embodiments, binder materials such as Al may be added to thecompositions described herein. For example, the materials employed intwin wire arc spray methods described herein may be wrapped with asheath such as mild steel, stainless steel, nickel, nickel chrome, oraluminum such that the resultant coating shows an increase in bondstrength. In some embodiments, an amorphous or nanocrystalline coatingproduced using the twin wire arc spray method manufactured using a mildsteel, stainless steel, nickel, or nickel chrome sheath resulted in bondstrengths exceeding 8000 psi as measured by ASTM C 633. In furtherembodiments, wrapping an Al sheath around a solid or cored wirecontaining Ni-base materials described herein also may result inincreased bond strengths. In additional embodiments, Al may be added toany material described herein in a range of concentrations. In theseembodiments, the other elements of the material will typically bereduced by a proportional amount so maintain their relativeconcentrations. For example, Al may be added in concentrations of0.5-10% to form materials having components defined by:

(1)(Fe₆₂₋₆₆Cr₁₃₋₁₄(Mo,Nb)₈₋₁₂(C,B)_(4.2-4.4)Ni_(4.8)Si_(0-1.2)Mn_(0-1.2)W_(0-3.8))_(100-x)Al_(x)

(2)(Fe₆₇₋₆₉Cr_(9.6-10.9)(Mo,Nb)_(9.2-10.6)C_(1.4-2.1)B_(1.6-1.8)Si_(0-0.2)Ti_(0-0.2)W_(7.3-9))_(100-x)Al_(x)

(3)(Fe₆₇₋₇₁Cr_(9.6-9.7)Mo_(8.8-10.5)C_(1.8-2.2)B_(1.4-1.6)W_(7.4-8.8))_(100-x)Al_(x)

(4)(Fe₄₃₋₅₃Cr_(5.7-7.2)(Mo,Nb)_(6.6-15.5)C_(1-0.3)B_(1.3-1.8)W_(9.98-28)Ti₁₋₇)_(100-x)Al_(x)

(5)(Fe₆₁₋₇₅Cr_(9-14.4)Ni_(0-4.8)(Mo,Nb)_(7.9-11.7)C_(1.6-2.1)B_(1.3-4.6)W_(0-9.98)Ti_(0.25-7)Si_(0-1.1)Mn_(0-1.1))_(100-x)Al_(x)

where x ranges from 0.5% to 10%. In a specific embodiment, increasedbond strengths occur in some applications where components are definedby the formula Fe₆₅₋₆₇Cr₁₁₋₁₃Nb₄₋₆B₄₋₅Ni₄₋₆Si_(0-0.5)Mn_(0-1.5)Al₁₋₃. Inparticular, the composition Fe₆₇Cr₁₃Nb₆B₄Ni₅Si₁Mn₁Al₂ demonstrated abond strength exceeding 10,000 psi. Accordingly, the addition of Al tomaterials described herein may further increase the materials' utilitiesin applications requiring high coating bond strength and abrasionresistance.

Certain materials disclosed in the present disclosure can be directedtoward weld overlay materials. In some embodiments, although they aresuitable for other weld overlay hardfacing applications, the materialsserve as a superior weld overlay material for the protection of tooljoints in oil and gas drilling operations.

Some embodiments comprise an iron-based alloy capable of forming a crackfree hardbanding weld overlay coating on a curved substrate of 6″ orsmaller without any pre-heating or slow cooling methods, resulting in a60+ Rockwell C surface. In further embodiments, when welded, the alloyhas a welded microstructure comprising a fine-grained ferritic matrixcontaining <10μm Nb and W carbide precipitates. In still furtherembodiments, the alloys may be magnetic or non-magnetic in nature.

Particular embodiments comprise alloys falling within the range ofalloys defined by the formula (In weight percent):Fe_(67.3-77.05)Cr₃₋₇Nb₄₋₇C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Ti₀₋₀₅Si_(0-0.5)Mn₀₋₂Ni₀₋₂.Other embodiments comprise alloys falling within the range of alloysdefined by the formula (In weight percent):Fe_(67.3-77.05)Cr₃₋₇Nb₄₋₇Co_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Ti_(0-0.5)Si_(0-0.5)Mn₀₋₆Ni₀₋₃.A specific embodiment comprises the alloy given by the formula (Inweight percent): Fe_(74.35)Cr₅Nb₄V₂B₁C_(0.8)W_(12.45)Si_(0.15)Ti_(0.25).Other embodiments comprise the alloy given by the formula (In weightpercent):B_(1.15-1.25)C_(1.0-1.1)Cr_(4.8-5.0)Fe_(bal)Mn_(<1.0)Nb_(4.0-4.2)Si_(<1.0)Ti_(0.2-0.3)V_(1.95-2.05)W_(12.4-12.5).Other embodiments comprise the alloy given by the formula (In weightpercent):B_(1.15-1.25)C_(1.0-1.1)Cr_(4.8-5.0)Fe_(bal)Mn_(<1.0)Nb_(0.4.0-4.2)Si_(<1.0)Ti_(0.2-0.3)V_(0.40-0.60)W_(8.8-9.2).

FIG. 18 illustrates a metal inert gas (MIG) weld bead of an alloyimplemented in accordance with an embodiment of the invention. Here,alloy 1800 comprised the alloy defined by the formula (In weightpercent):Fe_(67.3-77.05)Cr₃₋₇Nb₄₋₇C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Ti_(0-0.5)Si_(0-0.5)Mn₀₋₆Ni₀₋₃.The weld bead 1800 was applied to a 4140 steel 6″ diameter pipe 1801. Asmeasured using a liquid dye penetrant, the weld bead shoed no crackingor cross-checking.

In one embodiment, a microstructure of an alloy by the formula (Inweight percent): Fe_(74.35)Cr₅Nb₄V₂B₁C_(0.8)W_(12.45)Si_(0.15)Ti_(0.25)is provided. The microstructure of this alloy includes an optimizedmicrostructure with a ferrite matrix having fine-grained niobium andtungsten based precipitates. These precipitates are less than about 10μm on average and produce an alloy having a unique hardness andtoughness. The matrix is a fine-grained ferritic/austentic matrix whichis fully interconnected. The matrix is able to blunt cracking andprovides toughness to the overall material. The secondary phases and areextremely hard and are plentiful in the microstructure, forming up to30% by volume fraction, but are isolated from each other by theinterconnected matrix.

Three alloy compositions have been determined for manufacture intowelding wires for hardbanding testing. The alloys have been determinedfrom experimental results as part of an ongoing project to designhardbanding alloys, and subsequent laboratory analysis of potentialalloys compositions. Initial laboratory results suggested these alloysas ideal candidates and the experimental welding trials have beenconducted.

The alloy presented in this disclosure, namely,Fe_(74.35)Cr₅Nb₄V₂B₁C_(0.8)W_(12.45)Si_(0.15)Ti_(0.25), immediatelyshowed promise as the alloy formed a crack free weld overlay on a 6″round pipe without the use of a pre-heating step. Further analysis,including independent verification of a crack-free weld, and wearperformance, indicated that the weld alloy represented a technologicaladvance to currently used alloys and materials for use in oil and gasdrilling.

The alloys presented in this disclosure offer many unique advantages tocurrently available weld overlay alloys, which when simultaneouslyutilized provide substantial benefit to the oil and gas drillingoperation. Previously, no other single alloy could offer all thesebenefits to the hardbanding process and operation. Some of theadvantages that embodiments of the invention present include thefollowing.

First, crack-free as deposited welds: The alloys disclosed can be weldedonto curved surfaces without the use of pre-heating or slow coolingtechniques, and form a continuous crack free weld bead. The lack ofpre-heating required is very advantageous not only because it eliminatesan extra step in the process, but it prevents the possible deteriorationof the inner polymer coating which is commonly used in drill pipes andis subject to failure when the pipe is pre-heated. Slow cooling is alsoa step which is generally unavailable to hardbanding done in the field,and it is advantageous if it is not required. Previously, thesecapabilities could be achieved only with weld overlay alloys that hadsubstantially lower surface hardness levels.

Second, ability to be welded over itself and other weld beads withoutcracking: Weld overlays metallurgically bond to the substrate materialand form a novel diluted alloy which is partially the original weldingalloy and partially the substrate base material alloy. This dilutioneffect create different weld compositions depending upon the base metalthat it is being welded onto. In the practice of oil drillinghardbanding it is common to re-weld over the top of a weld bead once ithas partially worn away. In the case of many hardbanding alloys, thisre-welding creates enough of a compositional shift in the weld whencompared to welding atop of the original un-welded part, that crackingoccurs in the re-weld whereas none occurred in the original weld. Thealloys presented in this patent are have sufficient crack resistant suchthat they can be welded atop previous welds and experience no cracking.Previously, this capability could be achieved only with weld overlayalloys that result in substantially lower surface hardness levels.

Third, high hardness: The alloys described in this patent containhardness levels of 60 Rockwell C or higher in the diluted condition whenwelded onto 4140 steel pipe under conditions similar to those used inthe field application of hardbanding alloys for tool joints. Typicalhardbanding alloys report 60+ Rockwell C values only when measured inthe undiluted condition. However, in actual single pass weld overlayswith significant dilution, which is the condition used for theseapplications, these alloys experience lower hardness values.

Fourth, improved wear resistance: The alloys described in this patentpossess improved wear resistance compared to the previously mostadvanced hardbanding alloys used in oil and gas drilling operations. Thewear resistance is measured using the ASTM G65 dry sand wear test. Thewear loss of this alloy in the diluted condition (the conditiontypically used in the actual oil and gas drilling operations) was 0.1092grams lost, significantly better than previous technologies which reportun-diluted (condition resulting in lower wear losses, and not acondition used in the field) 0.12 g lost.

Fifth, the ability to absorb excess carbon with no or limited cracking:The alloys described in this patent are compositionally designed to forma high fraction of finely grained carbide precipitates. Thethermodynamics inherent to these alloys allow for excess carbon to beabsorbed into the weld without altering the advantageous microstructure,resulting in no or minimal cracking. This effect is advantageous in thehardbanding industry as a MIG carbide process is typically used tocreate hardbanding weld beads. In this process, WC/Co particles (˜1 mmin size) are fed into the weld bead as the weld is being made. Thisprocess creates a very difficult substrate to weld atop as there is alarge concentration of W and C which will be introduced into there-welded composition and microstructure. Previously used hardbandingalloys would experience drastic changes in microstructure and propertiesas a result of being re-welded onto this particular substrate. However,the designed chemistry of the alloy presented in this patent areflexible enough to absorb the excess carbon and tungsten and seerelatively small changes in microstructure and properties. Thus, evenwhen welded onto a un-worn MIG-carbide weld bead, they will experienceonly slight cross checking.

Sixth, optimal microstructure for limited casing wear: In drillingoperations, the hardbanding weld beads constantly rub and wear againstthe outer casing. It is very critical that the hardbanding weld bead notwear away sufficiently against the casing so as to cause casing failure.Alloys which do not result in extreme casing wear are termed, ‘casingfriendly’. Early hardbanding techniques such as MIG carbide, wherecoarse carbide grains were introduced into the weld, resulted in extremecasing wear and proved unacceptable in drilling operations where acasing was a requirement. The MIG carbide welds are formed of a softsteel matrix containing large carbide grains. The wear behavior is suchthat the steel quickly wears a way leaving the sharp carbide particlesto gouge away at the casing. In the alloys presented in this patent, thecarbide particles are very fine and evenly distributed so as not tocause highly localized regions of wear on the casing. Furthermore, thematrix is a hardened fine-grained structure, which exhibits hardeningaccording to the Hall-Petch relationship. Thus, the casing will be incontact with a relatively smooth surface as opposed to a weld bead withsharp hard particles which locally wear and cause casing failure.

Some embodiments of hardbanding materials comprise alloys falling withinthe range of alloys defined by the formula (In weight percent):Fe_(65.3-79.95)Cr₃₋₇Ni₀₋₆Mn₀₋₆Nb_(3.5-7)V_(0-2.05)C_(0.5-1.5)B_(0.6-1.75)W_(7.5-15.45)Si_(0-1.0)Ti₀₋₁Al₀₋₄.Particular embodiments comprise alloy defined by the formulae (in weightpercent):Fe_(65.3-79395)Cr₃₋₇Ni₀₋₆Nb_(3.5-6)V₀₋₂C_(0.8-1.5)B_(0.8-1.4)W_(8.5-13.5)Si_(0.15)Ti_(0.25-1)Al₀₋₄;Fe_(bal)Cr_(4.8-5.2)Mn_(<1.1)Nb_(0.4.0-4.4)C_(1.0-1.1)V_(0.40-2.8)B_(0.8-1.25)W_(7.5-9.2)Si_(<1.0)Ti_(0.2-0.3);orFe_(bal)Cr_(5.1)Mn_(1.1)Nb_(4.3)C_(1.1)V_(2.7)B_(0.8)W_(7.6)Si_(0.5)Ti_(0.2).Weight percents of various constituent elements in some exemplaryembodiments falling within the range are listed in the following table:

Alloy ID Fe Cr Ni Mn Nb V C B W Si Ti Al H5A 71.35 5 0 2 4 2 0.8 1 13.450.15 0.25 0 H5B 67.3 5 0 6 4 2 0.85 1 13.45 0.15 0.25 0 H5C 71.3 5 2 0 42 0.85 1 13.45 0.15 0.25 0 H5D 67.3 5 6 0 4 2 0.85 1 13.45 0.15 0.25 0H5E 65.3 5 2 6 4 2 0.85 1 13.45 0.15 0.25 0 H5F 65.3 5 6 2 4 2 0.85 113.45 0.15 0.25 0 H5G 72.65 5 0 0 4 2 1.3 1.2 13.45 0.15 0.25 0 H5H72.65 5 0 0 4 2 1.5 1 13.45 0.15 0.25 0 H5I 72.85 5 0 0 4 2 1.5 0.813.45 0.15 0.25 0 H5J 72.15 5 0 0.5 4 2 1.1 1.4 13.45 0.15 0.25 0 H5K77.3 5 0 0 4 2 0.8 1 9.5 0.15 0.25 0 H5L 75.5 5 0 0 4 2 1 1.1 11 0.150.25 0 H5M 73.25 5 2 0 4 2 0.85 1 11.5 0.15 0.25 0 H5N 75.25 5 0 0 6 20.85 1 9.5 0.15 0.25 0 H5O 75.25 5 2 0 4 2 0.85 1 9.5 0.15 0.25 0 H5P75.3 5 2 0 4 2 1 0.8 9.5 0.15 0.25 0 H5Q 70.8 5 2 0.5 4 2 0.85 1 13.450.15 0.25 0 H5R 73.3 5 2 0 6 2 1 0.8 9.5 0.15 0.25 0 H5S 73.8 5 3 0.5 42 1 0.8 9.5 0.15 0.25 0 H5T 72.8 5 4 0.5 4 2 1 0.8 9.5 0.15 0.25 0 H5U66.9 5 6 0 4 2 1.4 0.8 13.5 0.15 0.25 0 H5V 72.3 5 3 2 4 2 1 0.8 9.50.15 0.25 0 H5W 73.3 5 3 1 4 2 1 0.8 9.5 0.15 0.25 0 H5X 72.1 5 3 2 4 21.2 0.8 9.5 0.15 0.25 0 H5Y 71.9 5 3 2 4 2 1.4 0.8 9.5 0.15 0.25 0 H5&70.1 5 3 2 4 2 1.2 0.8 11.5 0.15 0.25 0 H5Z 70.9 5 6 0 4 2 1.4 0.8 9.50.15 0.25 0 H7A 78.75 5 0 0 4 0.25 1 1.1 9.5 0.15 0.25 0 H7B 79 5 0 0 40 1 1.1 9.5 0.15 0.25 0 H7C 76.75 5 0 0 4 0.25 1 1.1 9.5 0.15 0.25 2 H7D74.75 5 0 0 4 0.25 1 1.1 9.5 0.15 0.25 4 H7E 78.75 5 0 0 4 0 1 1.1 9.50.15 0.5 0 H7F 78.25 5 0 0 4 0 1 1.1 9.5 0.15 1 0 H7G 78.5 5 0 0 4 0.5 11.1 9.5 0.15 0.25 0 H7H 78.55 5 0 0 4 0 1.2 1.1 9.5 0.15 0.5 0 H7I 78.855 0 0 4 0.25 1.2 0.8 9.5 0.15 0.25 0 H7J 78.75 5 0 0 4 0 0.8 1.3 9.50.15 0.5 0 H7K 78.95 5 0 0 4 0.25 1 0.9 9.5 0.15 0.25 0 H7L 78.55 5 0 04 0.5 0.9 1.4 9 0.15 0.5 0 H7M 77.95 5 0 0 4 0.5 1 1.4 9.5 0.15 0.5 0H7N 79.65 5 0 0 4 0 1.1 1.1 8.5 0.15 0.5 0 H7O 79.3 5 0 0 4 0 1 0.8 9.50.15 0.25 0 H7P 79.9 5 0 0 4 0 1 1.2 8.5 0.15 0.25 0 H7Q 79.95 5 0 0 40.25 1 0.9 8.5 0.15 0.25 0 H7R 79.75 5 0 0 4 0.25 1.1 1 8.5 0.15 0.25 0H7S 79.85 5 0 0 3.5 0.25 1.1 0.9 9 0.15 0.25 0 H7T 78.65 5 0 0 4.5 0.251.1 1.1 9 0.15 0.25 0 H7U 78 5 0 0 4.5 0.5 1 1.1 9.5 0.15 0.25 0 H7V78.75 5 0 0 4.5 0.25 1 1.1 9 0.15 0.25 0 H7W 79 5 0 0 3.5 0.5 1 1.1 9.50.15 0.25 0 H7X 78.75 5 0 0 4.5 0.25 1.1 1 9 0.15 0.25 0 H7Y 78.3 5 0 04.5 0.25 1.1 1.2 9 0.15 0.5 0 H7Z 78.25 5 0 0 4.5 0.25 0.9 1.2 9.5 0.150.25 0 CF-1 76.62 5.12 0 1.08 4.27 2.69 1.07 0.82 7.61 0.52 0.2 0

FIG. 19 is a diagram depicting an alloy design process 1900 according tocertain aspects of the present disclosure. The alloy design processcomprises a 4-component metallic glass modeling technique based ontopology, liquidus temperature, chemical short range order and elasticstrain to determine an amorphous forming epicenter composition. Anamorphous forming composition epicenter 2010 and an associated amorphousforming composition range 2020 are shown in diagram 2000 of FIG. 20.Various aspects of such a 4-component metallic glass modeling techniqueare described above in the present disclosure and also in University ofCalifornia, San Diego Ph.D dissertation “Modeling the Glass FormingAbility of Metals” by Justin Lee Cheney, which is incorporated byreference herein for all purposes. The modeling technique can be used tomaximize the potential for amorphous forming ability for the design ofan amorphous material 1920 having a metallic glass epicentercomposition.

After determining an amorphous forming epicenter composition, a variantcomposition having a predetermined change in constituent elements fromthe amorphous forming epicenter composition is determined, and an alloyhaving the variant composition is formed and analyzed.

For example, a first or second variant technique 1930 or 1940 may beemployed to design a thermal spray material (e.g., glass/crystalcomposite 1950) for use as a thermal spray wire or a fine-grainedcrystalline material (e.g., μm-structured crystalline 1960) for use as aweld overlay material, respectively.

A. Design of a Thermal Spray Material

The first variant technique 1930 for designing a thermal spray material(e.g., glass/crystal composite structures 1950) involves vitrificationpotential determination 1932 and solidification analysis 1934.

With regard to the vitrification potential determination 1932, in orderto design glass/crystal composites, one or more variant compositionsranging from between about 5 and 10% atomic percent offset inconstituent elements from an amorphous forming composition epicenter2010 are chosen. As used herein, the term “about” means within normalmanufacturing tolerances. This range is termed nanocrystalline/glasscomposite zone 2030 in diagram 2000 shown in FIG. 20. A variantcomposition in this nanocrystalling/glass composite zone can include oneor more additional components that are not present in the amorphousforming epicenter composition. In certain embodiments, the variantcomposition includes between about 0.1 and 10% additional constituentthat is not present in the amorphous forming epicenter composition.

The solidification analysis 1934 can be performed through a lab-basedtechnique to simulate the cooling rate in thermal spray materials thusdetermined. In an exemplary setup 2108, an homogeneous alloy ingot ismelted within an arc melter such as the one shown in FIG. 21 in a watercooled copper cavity 2107. When a fully molten copper plate 2105, termedthe splat block, is dropped onto the liquid alloy ingot 2106, the liquidalloy ingot is rapidly cooled in the form of a thin sheet (between about0.25 and 1 mm) in thickness. The resulting compositenanocrystalline/glass microstructure can be evaluated using any knownstructural analysis methods including, but not limited to, XRD and SEManalysis. Those variant compositions that satisfy certain conditions(e.g., hardness and structural integrity) are selected. Variantcompositions designed and selected through the processes described abovecan be produced as thermal spray wires, for instance.

B. Design of a μm Crystalline Structure (Weld Overlay Material)

The second variant technique 1940 for designing a fine-grainedcrystalline material (e.g., μm-structured crystalline 1960) can involvea phase diagram prediction 1942 and a phase chemistry prediction 1944.

In the phase diagram prediction 1942, specific alloying elements areeither added or subtracted to encourage an evolution of desiredcrystalline phases in the microstructure as illustrated by phase diagram2200 shown in FIG. 22. The phase chemistry prediction 1944 can be usedto model any shifts in elemental concentration of the liquid as primarycrystallites nucleate.

Analysis of composition behavior is completed using specially designedexperimental lab-based techniques to simulate the cooling rate of theweld. FIG. 23 illustrates an exemplary alloy formation and analysisprocedure. In the procedure, an homogeneous alloy ingot is melted, e.g.,within an arc melter in a water cooled copper cavity. Size of thehomogenous alloy ingot being melted (“melt”) is preferably between about10 and 20 g to ensure that the cooling rate closely matches thatexperienced in MIG welding. FIG. 24 is a diagram 2400 depicting liquidcomposition versus cooling curves for various constituent compositions.Certain variant compositions designed, analyzed and selected through theprocesses described above can be produced as welding wires, forinstance.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for theinvention, which is done to aid in understanding the features andfunctionality that can be included in the invention. The invention isnot restricted to the illustrated example architectures orconfigurations, but the desired features can be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations can be implementedto implement the desired features of the present invention. Also, amultitude of different constituent module names other than thosedepicted herein can be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the invention is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherembodiments of the invention, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

1. An iron-based alloy having a microstructure comprising a fine-grainedferritic matrix and having a 60+ Rockwell C surface, wherein theferritic matrix comprises <10 μm Nb and W carbide precipitates.
 2. Thealloy of claim 1, given by the chemical formula (In weight percent):Fe_(65.3-79.95)Cr₃₋₇Ni₀₋₆Mn₀₋₆Nb_(3.5-7)V_(0-2.8)C_(0.5-1.5)B_(0.6-1.75)W_(7.5-15.45)Si_(0-1.0)Ti_(0-1.0)Ti₀₋₁Al₀₋₄.3. The alloy of claim 2, given by the chemical formula (In weightpercent):Fe_(65.3-79.95)Cr₅Ni₀₋₆Mn₀₋₆Nb_(3.5-6)V₀₋₂C_(0.8-1.5)B_(0.8-1.4)W_(8.5-13.5)Si_(0.15)Ti_(0.25-1)Al₀₋₄.4. The alloy of claim 2, given by the chemical formula (In weightpercent):Fe_(67.3-77.05)Cr₃₋₇Ni₀₋₃Mn₀₋₂Nb_(3.5-7)C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Si_(0-0.5)Ti_(0-0.5).5. The alloy of claim 4, given by the chemical formulas (in weightpercent): Fe_(74.35)Cr₅Nb₄V₂C_(0.8)B₁WE_(12.45)Si_(0.15)Ti_(0.25). 6.The alloy of claim 2, given by the chemical formula (In weight percent):Fe_(67.3-77.05)Cr₃₋₇Ni₀₋₃Mn₀₋₆Nb₄₋₇C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Si_(0-0.5)Ti_(0-0.5).7. The alloy of claim 2, given by the chemical formula (In weightpercent):Fe_(bal)Cr_(4.8-5.0)Mn_(<1.0)Nb_(0.4-4.2)C_(1.0-1.1)V_(1.95-2.05)B_(1.15-1.25)W_(12.4-12.5)Si_(<1.0)Ti_(0.2-0.3).8. The alloy of claim 2, given by the chemical formula (In weightpercent):Fe_(bal)Cr_(4.8-5.2)Mn_(<1.1)Nb_(0.4.0-4.4)C_(1.0-1.1)V_(0.40-2.8)B_(0.8-1.25)W_(7.5-9.2)Si_(<1.0)Ti_(0.2-0.3).9. The alloy of claim 2, given by the chemical formula (In weightpercent):Fe_(bal)Cr_(5.1)Mn_(1.1)Nb_(4.3)C_(1.1)V_(2.7)B_(0.8)W_(7.6)Si_(0.5)Ti_(0.2).10. A method of welding, comprising forming a crack free hardbandingweld overlay coating with an iron-based alloy having a microstructurecomprising a fine-grained ferritic matrix and having a 60+ Rockwell Csurface, wherein the ferritic matrix comprises <10.1μm Nb and W carbideprecipitates.
 11. The method of claim 10, wherein the alloy is given bythe chemical formula (In weight percent):Fe_(65.3-79.95)Cr₃₋₇Ni₀₋₆Mn₀₋₆Nb_(3.5-7)V_(0-2.8)C_(0.5-1.5)B_(0.6-1.75)W_(7.5-15.45)Si_(0-1.0)Ti₀₋₁Al₀₋₄.12. The method of claim 11, wherein the alloy is given by the chemicalformula (In weight percent):Fe_(67.3-77.05)Cr₃₋₇Ni₀₋₃Mn₀₋₂Nb_(3.5-7)C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Si_(0-0.5)Ti_(0-0.5).13. The method of claim 11, wherein the alloy is given by the chemicalformula (In weight percent):Fe_(67.3-77.05)Cr₃₋₇Ni₀₋₃Mn₀₋₂Nb_(3.5-7)C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Si_(0-0.5)Ti_(0-0.5).14. The method of claim 13, wherein the alloy is given by the chemicalformulas (in weight percent):Fe_(74.35)Cr₅Nb₄V₂C_(0.8)B₁W_(12.45)Si_(0.15)Ti_(0.25).
 15. The methodof claim 11, wherein the alloy is given by the chemical formula (Inweight percent):Fe_(67.3-77.05)Cr₃₋₇Ni₀₋₃Mn₀₋₆Nb₄₋₇C_(0.5-1.4)B_(0.6-1.75)W_(9.5-15.45)Si_(0-0.5)Ti_(0-0.5).16. The method of claim 11, wherein the alloy is given by the chemicalformula (In weight percent):Fe_(bal)Cr_(4.8-5.0)Mn_(<1.0)Nb_(0.4.0-4.2)C_(1.0-1.1)V_(1.95-2.05)B_(1.15-1.25)W_(12.4-12.5)Si_(<1.0)Ti_(0.2-0.3).17. The method of claim 11, wherein the alloy is given by the chemicalformula (In weight percent):Fe_(bal)Cr_(4.8-5.2)Mn_(<1.1)Nb_(0.4.0-4.4)C_(1.0-1.1)V_(0.4-2.8)B_(0.8-1.25)W_(7.5-9.2)Si_(<1.0)Ti_(0.2-0.3).18. The method of claim 11, wherein the alloy is given by the chemicalformula (In weight percent):Fe_(bal)Cr_(5.1)Mn_(1.1)Nb_(4.3)C_(1.1)V_(2.7)B_(0.8)W_(7.6)Si_(0.5)Ti_(0.2).19-29. (canceled)